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Mohamed Elchalakani - One of the best experts on this subject based on the ideXlab platform.
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behaviour and design of cold formed chs under static Pure Bending through finite element analysis
Thin-walled Structures, 2020Co-Authors: Chenpu Guo, Ali Karrech, Mohamed Elchalakani, Michael Richard Bambach, Bo YangAbstract:Abstract The current slenderness limits are significantly different in international design codes for cold-formed Circular Hollow Sections (CHS) under Pure Bending. This paper aims to use the Finite Element (FE) method to understand the behaviour of cold-formed CHS under Pure Bending and to propose new design rules. The model is calibrated by comparing its predicted load-deflection curves with previously published experimental data. In total, 21 specimens were modelled with diameter-to-thickness ratios ranging from 13 to 122. The current slenderness limits in the present international steel specifications were examined using the FE model and their suitability for cold-formed CHS is discussed. The effect of section slenderness on rotation capacity has been examined where the predicted variation of rotation capacity against section slenderness has been compared to the experimental results. A new equation for the amount of initial geometrical imperfection as a function of section slenderness has been developed and proposed for design purposes. The ovalisation deformation ratio and the critical strain at local buckling were determined and compared for compact, non-compact and slender sections. The progressive Bending deformations of CHS at 10 critical steps have been presented and compared for the three cross sectional types, in particular at the maximum moment and Bending rotation. In general, a good agreement has been obtained between the predicted strengths and ductilities using the current FE models and those of the experimental data of cold-formed CHS.
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The prediction of ultimate Pure Bending moment of concrete-filled steel tubes by adaptive neuro-fuzzy inference system (ANFIS)
Neural Computing and Applications, 2019Co-Authors: Hakan Basarir, Mohamed Elchalakani, Ali KarrechAbstract:In this study, different modelling techniques such as multiple regression and adaptive neuro-fuzzy inference system (ANFIS) are used for predicting the ultimate Pure Bending of concrete-filled steel tubes (CFTs). The behaviour of CFT under Pure Bending is complex and highly nonlinear; therefore, forward modelling techniques can have considerable limitations in practical situations where fast and reliable solutions are required. Linear multiple regression (LMR), nonlinear multiple regression (NLMR) and ANFIS models were trained and checked using a large database that was constructed and populated from the literature. The database comprises 72 Pure Bending tests conducted on fabricated and cold-formed tubes filled with concrete. Out of 72 tests, 48 tests were conducted by the second author. Input variables for the models are the same with those used by existing codes and practices such as the tube thickness, tube outside diameter, steel yield strength, strength of concrete and shear span. A practical application example, showing the translation of constructed ANFIS model into design equations suitable for hand calculations, was provided. A sensitivity analysis was conducted on ANFIS and multiple regression models. It was found that the ANFIS model is more sensitive to change in input variables than LMR and NLMR models. Predictions from ANFIS models were compared with those obtained from LMR, NLMR, existing theory and a number of available codes and standards. The results indicate that the ANFIS model is capable of predicting the ultimate Pure Bending of CFT with a high degree of accuracy and outperforms other common methods.
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Plastic and yield slenderness limits for circular concrete filled tubes subjected to static Pure Bending
Thin-walled Structures, 2016Co-Authors: Mohamed Elchalakani, Mostafa Fahmi Hassanein, Ali Karrech, Bo YangAbstract:Abstract The current slenderness limits in international design codes are often based on certain rotation capacities obtained from plastic Bending tests of Concrete Filled Tubes (CFT). In the past, a plastic slenderness limit of λs=188 was obtained by the first author based on a fracture rotation limit of the steel tube. However, such limit may be questionable being brittle and insufficient for plastic design of CFT members, sub-assemblies and frames where adequate strain/deformation ductility is required. The main aims of this paper are to present (i) a new method to determine new ductile slenderness limits suitable for plastic design of structures based on the measured strains in plastic Bending tests on CFT; (ii) a closed-form solution for the elastic and inelastic buckling strains of CFT under Pure Bending using a new simplified energy approach employing the well-known Ritz method. The critical strains obtained from such analysis were used to derive new slenderness limits for CFT; and (iii) finite element modelling of CFT and compare the experimental and numerical moment-rotation responses. The effect of concrete filling on the post-buckling strength of restrained tubes is quantified. The current design rules for unrestrained Circular Hollow Sections (CHS) in steel specifications are also compared with the restrained strength obtained from the tests. Two new compact and yield slenderness limits were derived based on the strength corresponds to the appearance of the plastic ripples during the test. The experimentally obtained and the theoretically derived slenderness limits are compared against the available limits in the design codes and standards. The newly derived compact limit of λp=79 was found in a good agreement with λp=72 specified for CFT in the ANSI/AISC 360-10 specification. However, the new yield limit of λy=150 was found considerably lower than λy=254 for CFT specified in the ANSI/AISC 360-10.
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finite element analysis of cft columns subjected to Pure Bending moment
Steel and Composite Structures, 2010Co-Authors: Mohamed ElchalakaniAbstract:Proper material constitutive models for concrete-filled tube (CFT) columns of circular cross section and subjected to Pure Bending moment are proposed. These material models are implemented into the Abaqus finite element program and verified against experimental data. It has been shown that the steel tube does not provide good confining effect to the concrete core when the CFT columns is subjected to Pure Bending moment. When the diameter-to-thickness ratio of the CFT columns is small, the behavior of the CFT column is the same as the steel tube without a concrete core.
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neural networks for modelling ultimate Pure Bending of steel circular tubes
Journal of Constructional Steel Research, 2008Co-Authors: Mohamed A Shahin, Mohamed ElchalakaniAbstract:The behaviour of steel circular tubes under Pure Bending is complex and highly nonlinear. The literature has a number of solutions to predict the response of steel circular tubes under Pure Bending; however, most of these solutions are complicated and difficult to use in routine design practice. In this paper, the feasibility of using artificial neural networks (ANNs) for developing more accurate and simple-to-use models for predicting the ultimate Pure Bending of steel circular tubes is investigated. The data used to calibrate and validate the ANN models are obtained from the literature and comprise a series of 49 Pure Bending tests conducted on fabricated steel circular tubes and 55 tests carried out on cold-formed tubes. Multilayer feed-forward neural networks that are trained with the back-propagation algorithm are constructed using four design parameters (i.e. tube thickness, tube diameter, yield strength of steel and modulus of elasticity of steel) as network inputs and the ultimate Pure Bending as the only output. A sensitivity analysis is conducted on the ANN models to investigate the generalization ability (robustness) of the developed models, and predictions from the ANN models are compared with those obtained from most available codes and standards. To facilitate the use of the developed ANN models, they are translated into design equations suitable for spreadsheet programming or hand calculations. The results indicate that ANNs are capable of predicting the ultimate Bending capacity of steel circular tubes with a high degree of accuracy, and outperform most available codes and standards.
Raphael H. Grzebieta - One of the best experts on this subject based on the ideXlab platform.
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Strength of circular hollow sections (CHS) tubular beams externally reinforced by carbon FRP sheets in Pure Bending
Thin-walled Structures, 2009Co-Authors: Jimmy Haedir, Michael Richard Bambach, Xiao Ling Zhao, Raphael H. GrzebietaAbstract:Particular structural forms such as circular tubular sections when under load may experience premature local buckling of the steel component, attributable to the thin-walled nature of the section. The use of high-strength advanced composite materials tends to accompany the minimum of structural weight, and is hence presently being assessed for effectiveness as supplementary external reinforcing materials. Composite beams of fibre-reinforced polymers (FRP) and steel, formed as tubular steel sections externally reinforced by thin-bonded carbon FRP (CFRP) sheets, exhibit many phenomena not found in conventional structural steel components, and these can have a marked bearing both on the behaviour of members composed of these materials and, by connotation, on the way in which such members are designed. The potential identification of CFRP reinforcement incorporated onto steel circular hollow section (CHS) beams has not been adequately explored, particularly in Pure moment regions. This paper provides an experimental study consisting of CHS beams reinforced by CFRP sheets under Pure Bending. The role of the composite reinforcement is to interact with the enveloped steel component and to restrain the section to deform in a favourable fashion for strength enhancement. It is shown how these sections exploit the best attributes of both reinforcing fibres and steel, conferring greater strength to CHS beams made with thin-walled steel sections. The tests reveal that the strength of composite beams is influenced mainly by the amount of fibre reinforcement and the orientation of fibre skin. Also presented in this paper is an analytical method employing the modular ratio concept and considering the sectional slenderness limits of AS 4100 for evaluation of the strength of CFRP-reinforced CHS beams.
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variable amplitude cyclic Pure Bending tests to determine fully ductile section slenderness limits for cold formed chs
Australian Structural Engineering Conference 2005, 2005Co-Authors: Mohamed Elchalakani, Xiao Ling Zhao, Raphael H. GrzebietaAbstract:In related papers, the authors have successfully determined the plastic limit (λp=60) that defines a compact section for CHS beams from monotonic Pure Bending tests (Elchalakani et al 2002a,b). In a recent paper, the authors have determined the fully ductile slenderness limits λfd=60,45,39 and 34 suitable for seismic design that correspond to structural ductility indices μs=4.8,6.4,8.0 and 9.6 respectively (Elchalakani et al 2004) from constant amplitude cyclic loading tests to NZS 4203 (1992). The present paper attempts to determine new fully ductile sections suitable for seismic design from variable amplitude cyclic Pure Bending tests. This paper examines experimentally as-received compact, cold-formed CHS beams with section slenderness in the range of D/t = 20 to 40. The tubes were tested to destruction under variable amplitude cyclically applied Bending rotations simulating moderate to sever earthquake-type oscillations. A total of 9 CHS beams were subjected to a cyclic loading to a similar protocol as specified in AISC (2002). The fully ductile section slenderness limits for cold-formed CHS were derived based on the test results. These limits are compared with previously derived static and seismic limits. Comparisons of the seismic and static slenderness limits are also made based on the values specified in the current design rules including those in the USA (AISC 2002; AISC 2000) and Japan (AIJ 1990; JRA 1996).
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plastic collapse analysis of slender circular tubes subjected to large deformation Pure Bending
Advances in Structural Engineering, 2002Co-Authors: Mohamed Elchalakani, Raphael H. Grzebieta, Xiao Ling ZhaoAbstract:This paper presents a plastic mechanism analysis for thin-walled circular hollow section (CHS) tubes deforming in a multi-lobe or diamond collapse mode under large deformation Pure Bending. The fold formation process was such that the shell curvature flattened on the compression side transforming into a definite number of flat triangles attached to each other. The collapse proceeded progressively by folding about the base and sides of these triangular planes and over traveling hinge lines. The collapse mechanism was similar to the diamond crush mode. An existing kinematic model for an axially compressed thin-walled circular tube was modified to predict the collapse curve of a thin-walled tube under Bending. Inextensional deformation and rigid plastic material behaviour were assumed in the derivation of the deformation energy. Ovalisation was observed during the test and its deformation energy was determined and found significant. An expression for the plastic collapse moment was obtained by equating the t...
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plastic mechanism analysis of circular tubes under Pure Bending
International Journal of Mechanical Sciences, 2002Co-Authors: Mohamed Elchalakani, Xiao Ling Zhao, Raphael H. GrzebietaAbstract:Abstract There are a number of solutions available to predict the response of a circular steel tube under Pure Bending. However, most of these solutions are based on an elasto-plastic treatment, which is complex and difficult to use in any routine design. This paper describes a theoretical treatment to predict the moment-rotation response of circular hollow steel tubes of varying D / t ratios under Pure Bending. The Mamalis et al. (J. Mech. Sci. 1989;203:411–7) kinematics model for a circular tube under a controlled moment gradient was modified to include the effect of ovalisation along the length of the tube. Inextensional deformation and rigid plastic material behaviour were assumed in the derivation of the deformation energy. The plasticity observed in the tests was assumed to spread linearly along the length of the tube. Two local plastic mechanisms (Star and Diamond shapes) were studied to model the behaviour observed in the tests especially during the unloading stage. The theoretical predictions are compared with the experimental results recently obtained by Elchalakani et al. (Quartral. J. Struct. Eng. 2000;3(3):1–16). Good agreement was found between the theoretical predictions and experimental moment-rotation responses, particularly for the Star shape mechanism. A closed-form solution is presented suitable for spreadsheet programming commonly used in routine design.
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concrete filled circular steel tubes subjected to Pure Bending
Journal of Constructional Steel Research, 2001Co-Authors: Mohamed Elchalakani, Xiao Ling Zhao, Raphael H. GrzebietaAbstract:Current design codes and standards provide little information on the flextural behaviour of circular concrete filled tubes (CFT) as there have been few experimental studies. There are significant differences in d/t-limits recommended in various codes for CFT under Bending. This paper presents an experimental investigation of the flexural behaviour of circular CFT subjected to large deformation Pure Bending where d/t = 12 to 110. The paper compares the behaviour of empty and void-filled, cold-formed circular hollow sections under Pure plastic Bending. It was found that for the range of d/t40, void filling prevented local buckling for very large rotations, whereas multiple plastic ripples formed in the inelastic range for specimens with 74d/t110. In general, void filling of the steel tube enhances strength, ductility and energy absorption especially for thinner sections. Based on the measured material properties, the plastic d/t-limit was found to be 112. A simplified formula is provided to determine the ultimate flexural capacity of CFT. The existing design rules for the ultimate moment capacity of CFT may be extended conservatively to a new slenderness range of 100ls 188. 2001 Elsevier Science Ltd. All rights reserved.
Barry S Myers - One of the best experts on this subject based on the ideXlab platform.
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comparative structural neck responses of the thor nt hybrid iii and human in combined tension Bending and Pure Bending
Stapp car crash journal, 2006Co-Authors: Alan T Dibb, Roger W Nightingale, Carol V Chancey, Lucy E Fronheiser, Laura Tran, Danielle Ottaviano, Barry S MyersAbstract:The biofidelity of both the Hybrid III and the THOR-NT anthropomorphic test device (ATD) necks in quasistatic tension-Bending and Pure-Bending were evaluated by comparing the responses of both the ATDs with results from validated computational models of the living human neck. Each ATD was tested using a variety of end-conditions to create the tension-Bending loads. The THOR-NT was tested both with and without muscle cables, and both with and without the central safety cable to test the effect of the cable on the behavior of the ATD. The Hybrid III was stiffer than the model for all tension-Bending end conditions. Quantitative measurement of the differences in response showed closer agreement between the THOR-NT and the model than the Hybrid III and the model. By contrast, no systematic differences were observed in the head kinematics. The muscle cables significantly stiffened the THOR-NT. The cables also shielded the occipital condyle upper neck load cell from a significant portion of the applied loads. The center safety cable significantly stiffened the response and decreased the fidelity, particularly in modes of loading in which models include post-mortem human surrogate (PMHS) response corridors while correcting for problems associated with cadaveric muscle.
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comparative structural neck responses of the thor nt hybrid iii and human in combined tension Bending and Pure Bending
Stapp car crash journal, 2006Co-Authors: Alan T Dibb, Roger W Nightingale, Carol V Chancey, Lucy E Fronheiser, Laura Tran, Danielle Ottaviano, Barry S MyersAbstract:This study evaluated the biofidelity of both the Hybrid III and the THOR-NT anthropomorphic test device (ATD) necks in quasistatic tension-Bending and Pure-Bending by comparing the responses of both the ATDs with results from validated computational models of the living human neck. This model was developed using post-mortem human surrogate (PMHS) osteoligamentous response corridors with effective musculature added (Chancey, 2005). Each ATD was tested using a variety of end-conditions to create the tension-Bending loads. The results were compared using absolute difference, RMS difference, and normalized difference metrics. The THOR-NT was tested both with and without muscle cables. The THOR-NT was also tested with and without the central safety cable to test the effect of the cable on the behavior of the ATD. The Hybrid III was stiffer than the model for all tension-Bending end conditions. Quantitative measurement of the differences in response showed more close agreement between the THOR-NT and the model than the Hybrid III and the model. By contrast, no systematic differences were observed in the head kinematics. The muscle cables significantly stiffened the THOR-NT by effectively reducing the laxity from the occipital condyle (OC) joint. The cables also shielded the OC upper neck load cell from a significant portion of the applied loads. The center safety significantly stiffened the response and decreased the fidelity, particularly in modes of loading in which tensile forces were large and Bending moments small. This study compares ATD responses to computational models in which the models include PMHS response corridors while correcting for problems associated with cadaveric muscle. While controversial and requiring considerable diligence, these kinds of approaches show promise in assessing ATD biofidelity.
S Rimovskis - One of the best experts on this subject based on the ideXlab platform.
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analysis of rectangular and circular cross section power hardening elements under Pure Bending
International Journal of Materials Engineering, 2013Co-Authors: S Rimovskis, Arturas SabaliauskasAbstract:Eng ineering theory of elastic plastic Bending is used in solving a grate variety of strength and durability problems. The accuracy of analysis depends on stress-strain curve idealizat ion model. The elastic linear hardening stress-strain relation is simp le and frequently used. But the actual stress-strain behaviour of ductile material in plastic reg ion is non-linear and, therefore, elastic power hardening material model is more p referab le. Moreover, the properties of monotonic tension and compression as proportional limits and parameters of hardening can differ. In this regard, analytical solution for rectangular and circular cross-section elements loading by monotonic elastic plastic Pure Bending is presented in the paper. The simp le power relation of stress and strain response is used. The equations describing deviation of the stress neutral axis fro m centroidal axis of an element and dimensionless Bending mo ment are derived.
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analysis of circular cross section element loaded by static and cyclic elastic plastic Pure Bending
International Journal of Fatigue, 2006Co-Authors: M Daunys, S RimovskisAbstract:Abstract Data of theoretical and experimental investigation of a circular cross-section element subjected to monotonic and cyclic elastic–plastic Pure Bending is presented in the paper. Linear approximation of monotonic and cyclic tension–compression curves was applied, what allowed to simplify analysis and to obtain satisfactory conformance of theoretical data with experimental results. Grade 45 structural steel specimens were subjected to low cycle stress or strain-controlled reversed tension–compression and cyclic Pure Bending. In case of strain-controlled loading low cycle fatigue life curves for both loading models (tension–compression and Bending) coincide. In case of stress-controlled Bending elastically deformed internal fibers of the element impede the plastic–strain accumulation in the external fibers, and in such a way decrease the quasi-static damage accumulation, and increase the lifetime. In this research specimens lifetime was calculated by use of fatigue damage fraction and quasi-static damage fraction summation rule. The damage calculations allowed to establish the increase of fatigue life at stress-controlled low cycle Bending.
Alan T Dibb - One of the best experts on this subject based on the ideXlab platform.
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comparative structural neck responses of the thor nt hybrid iii and human in combined tension Bending and Pure Bending
Stapp car crash journal, 2006Co-Authors: Alan T Dibb, Roger W Nightingale, Carol V Chancey, Lucy E Fronheiser, Laura Tran, Danielle Ottaviano, Barry S MyersAbstract:The biofidelity of both the Hybrid III and the THOR-NT anthropomorphic test device (ATD) necks in quasistatic tension-Bending and Pure-Bending were evaluated by comparing the responses of both the ATDs with results from validated computational models of the living human neck. Each ATD was tested using a variety of end-conditions to create the tension-Bending loads. The THOR-NT was tested both with and without muscle cables, and both with and without the central safety cable to test the effect of the cable on the behavior of the ATD. The Hybrid III was stiffer than the model for all tension-Bending end conditions. Quantitative measurement of the differences in response showed closer agreement between the THOR-NT and the model than the Hybrid III and the model. By contrast, no systematic differences were observed in the head kinematics. The muscle cables significantly stiffened the THOR-NT. The cables also shielded the occipital condyle upper neck load cell from a significant portion of the applied loads. The center safety cable significantly stiffened the response and decreased the fidelity, particularly in modes of loading in which models include post-mortem human surrogate (PMHS) response corridors while correcting for problems associated with cadaveric muscle.
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comparative structural neck responses of the thor nt hybrid iii and human in combined tension Bending and Pure Bending
Stapp car crash journal, 2006Co-Authors: Alan T Dibb, Roger W Nightingale, Carol V Chancey, Lucy E Fronheiser, Laura Tran, Danielle Ottaviano, Barry S MyersAbstract:This study evaluated the biofidelity of both the Hybrid III and the THOR-NT anthropomorphic test device (ATD) necks in quasistatic tension-Bending and Pure-Bending by comparing the responses of both the ATDs with results from validated computational models of the living human neck. This model was developed using post-mortem human surrogate (PMHS) osteoligamentous response corridors with effective musculature added (Chancey, 2005). Each ATD was tested using a variety of end-conditions to create the tension-Bending loads. The results were compared using absolute difference, RMS difference, and normalized difference metrics. The THOR-NT was tested both with and without muscle cables. The THOR-NT was also tested with and without the central safety cable to test the effect of the cable on the behavior of the ATD. The Hybrid III was stiffer than the model for all tension-Bending end conditions. Quantitative measurement of the differences in response showed more close agreement between the THOR-NT and the model than the Hybrid III and the model. By contrast, no systematic differences were observed in the head kinematics. The muscle cables significantly stiffened the THOR-NT by effectively reducing the laxity from the occipital condyle (OC) joint. The cables also shielded the OC upper neck load cell from a significant portion of the applied loads. The center safety significantly stiffened the response and decreased the fidelity, particularly in modes of loading in which tensile forces were large and Bending moments small. This study compares ATD responses to computational models in which the models include PMHS response corridors while correcting for problems associated with cadaveric muscle. While controversial and requiring considerable diligence, these kinds of approaches show promise in assessing ATD biofidelity.
